1. Field of the Invention
The present invention relates to a light-emitting diode also named LED lamp, and more particularly to a construction that houses the diode in a casing with improved thermal radiation efficiency suitable for driving it with a larger current to emit a large amount of light. In an exemplary application to a light source for a lamp that requires a relatively high brightness, such as a traffic signal, it can be achieved with a smaller number of LED lamps.
2. Description of the Related Art
To achieve a large amount of light output per light-emitting diode, a conventional construction intends to improve the efficiency of cooling an LED chip and drive it with a higher power. In such the construction, a thicker metal plate is applied to form part of a lead-frame that is employed to die-mount the LED chip thereon. In addition, one surface of the metal plate is exposed to external to dissipate the heat radiated from the LED chip directly to the atmosphere to achieve efficient cooling (for example, see Patent Document 1: Japanese Patent Application Laid-Open No. 2003-60240, paragraphs 0014–0027, FIGS. 1 and 5).
In the above-described conventional construction of the light-emitting diode lamp, the metal plate for use in formation of the lead-frame can exactly dissipate the heat radiated from the LED chip efficiently to external. The metal plate, however, transmits the external heat to the LED chip at the same efficiency.
In the conventional construction of the light-emitting diode lamp, the metal plate also has a function of terminal for supplying power to the LED chip. Accordingly, when the metal plate is connected to a power source by means of soldering, for example, the process heat is transmitted directly to the LED chip and heats the LED chip more than required, badly influencing on the lifetime of the LED chip possibly. This is a subject to be solved.